The traveling wave tube amplifier (TWTA) has become a key element in broadband microwave power amplification for radar and satellite communication. One advantage of the TWTA is the very high output power it provides. However, several drawbacks are associated with TWTAs, including short life-time, poor linearity, high cost, large size and weight, and the requirement of a high voltage drive, imposing high voltage risks.
Solid state amplifiers are superior to TWTAs in several aspects, such as cost, size, life-time and linearity. However, currently, the best available broadband solid state amplifiers can only offer output power in a watt range covering about 2 to 20 GHz frequency band. A high power solid state amplifier can be realized using power combining techniques. A typical corporate combining technique can lead to very high combining loss when integrating a large number of amplifiers. Spatial power combining techniques are implemented with the goal of combining a large quantity of solid-state amplifiers efficiently and improving the output power level so as be competitive with TWTAs.